The denominator of a fraction is 7 less than 3 times the numerator.  If the fraction is equivalent to $2/5$, what is the numerator of the fraction?
Explanation: We let the numerator be $x$, so the denominator is $3x-7$.  Because the fraction equals $2/5$, we have $x/(3x-7) = 2/5$.  Multiplying both sides by $5(3x-7)$ (or cross-multiplying) gives $5x = 2(3x-7)$.  Expanding the right side gives $5x = 6x - 14$.  Subtracting $6x$ from both sides gives $-x = -14$, so we find $x = \boxed{14}$.